Complex formation between EphB2 and Src requires phosphorylation of tyrosine 611 in the EphB2 juxtamembrane region.

The cellular components of the neuronal signaling pathways of Eph receptor tyrosine kinases are only beginning to be elucidated. Here we show that in vivo tyrosine phosphorylation sites of the Eph receptors EphA3, EphA4, and EphB2 in embryonic retina serve as binding sites for the Src-homology 2 (SH2) domain of Src kinase. Furthermore, tyrosine-phosphorylated EphB2 was detected in Src immunoprecipitates from transfected Cos cells, indicating that EphB2 and Src can physically associate. Interestingly, a form of Src with reduced electrophoretic mobility and increased tyrosine phosphorylation was detected in Cos cells expressing tyrosine-phosphorylated EphB2, suggesting a functional interaction between EphB2 and Src. Yeast two-hybrid analysis in conjunction with site-directed mutagenesis demonstrated that phosphorylated tyrosine 611 in the juxtamembrane region of EphB2 is crucial for the interaction with the SH2 domain of Src. In contrast, binding of the carboxy-terminal SH2 domain of phospholipase Cgamma was not abolished upon mutation of tyrosine 611 in EphB2. Phosphopeptide mapping of autophosphorylated full-length EphB2, and wild-type and tyrosine to phenylalanine mutants of the EphB2 cytoplasmic domain fused to LexA, showed tyrosine 611 in the sequence motif YEDP as a major site of autophosphorylation in EphB2. Our mutational analysis also indicated that tyrosines 605 and 611 are important for EphB2 kinase activity. We propose Src kinase as a downstream effector that mediates the neuron's response to Eph receptor activation.